Star Wars

Learn the latest technique for interfacing GM's OnStar system with aftermarket components.

It's been about five years since General Motors introduced their highly successful OnStar system in a few selected vehicles. The idea was to assist motorists and to increase revenue for GM. The OnStar system combines the long-range power of an analog cell phone with the speed and accuracy of GPS. Today's OnStar system uses courteous, personalized operators to facilitate services that include emergency and roadside assistance, map and travel help, unlocking doors, stolen vehicle tracking, and much more. Until recently, many car audio shops refused to place an aftermarket deck into an OnStar-equipped car because the factory deck is actually a vital part of the OnStar circuitry. This meant that serious car audiophiles who owned an OnStar system had to hang with the factory tunes. Until now!

Soundgate's STARMOD1
We talked with Rob Putman, owner of Soundgate (P.O. Box 6689, Sheridan, WY 82801 Phone 307-674-4707, FAX 307-674-4819 Web: www.soundgate.com) about their new STARMOD1 interface. Putman states, "Our most important consideration is to maintain all of the functions of the OnStar system. This means that we designed the STARMOD1 to sample the OnStar signal, process the information, and then feed the communications into a dedicated speaker, or into one of the car stereo speakers. Fully 100 percent of the OnStar functions are maintained with virtually any aftermarket deck."

How is it done? When the OnStar's blue (or red for emergency) button is pressed, the hidden cell phone connects the vehicle to OnStar's command center. The highly trained operator quickly identifies the specific vehicle and uses the GPS to fix an exact location. The factory stereo system is automatically muted and the OnStar operator initiates contact with the vehicle.

As soon as OnStar initiates contact with the vehicle, Soundgate's STARMOD1 picks up the signal — before it even gets into the factory deck. Then, rather than have the factory deck process the signal, the STARMOD1 takes over. This is how OnStar works without the factory deck. The correct OnStar wires have to be identified and connected to the STARMOD1, but installation time can be less than 15 minutes — even less when installed with a new aftermarket deck.

The STARMOD1 measures around 3 inches x 5 inches x 1 inch and has a constant +12-volt lead, chassis ground wire, two OnStar sensing input wires, a pair of speaker leads for the audio output, and a muting lead which provides +12 volts when the OnStar system is active. A green LED on the STARMOD1 indicates when the OnStar system is active. There's also a volume knob to adjust the level of the OnStar audio. Once set, the STARMOD1 unit can be stashed out of sight behind a glove box or under the dash. Since communications with the OnStar operator is via a Òhands-freeÓ cellular system, adjusting the receive audio volume is an important part of the installation. The STARMOD1 works both when the vehicle activates OnStar and if the OnStar operator wants to make contact with the vehicle.

Keeping the Factory Speakers
The audio output level of the STARMOD1 is sufficient to drive a 3.5-inch, 5.25-inch, 6.5-inch, or 6x9-inch speaker. Since the OnStar program material is always spoken word, any small speaker can handle the task. It's important that the dedicated OnStar speaker be installed away from the cell phone's 'hands-free' microphone.

There's a better idea than using a dedicated speaker for OnStar. Any one of the stereo system's speakers can be used, provided Soundgate's STARRELAY accessory is utilized. This 1-inch x 2-inch x 1-inch unit connects to the + and – terminals of a factory speaker, such as the front left speaker. The original speaker leads from the car audio system, and the speaker output leads from the STARMOD1, also connect to the STARRELAY unit. Then thereÕs a small black ground wire that connects to the car's chassis and a control lead that connects to the STARMOD1's muting output lead (Blue/White stripe).

The stereo system plays normally until the STARMOD1 detects OnStar activity. As soon as this occurs, the STARRELAY drops the regular program material and ONLY produces the OnStar audio. With the STARRELAY accessory, the STARMOD1 exactly duplicates the original functions with the original factory deck and speakers.

Installing the STARMOD1 and STARRELAY
We installed a Soundgate STARMOD1s and STARRELAYs into a late model Chevy pickup. The installation was simplified thanks to the great instructions and wiring diagrams included with each Soundgate product. We began by removing the factory deck. The new GM decks have a 9-pin connector that must be unplugged from the back of the factory deck. The STARMOD1's input wires connect to wire 11 (Brown/White) and wire 12 (Black/White) of this plug. We then extracted the factory deck.

The STARMOD1's black ground lead was wired to a clean section of the pickup's chassis. Next, we connected the fused Red lead from the STARMOD1 to the pickup's + 12 volts DC constant at the fuse box. It's important to wire the STARMOD1 to + 12 volts DC constant so that the OnStar can also operate when the vehicle's ignition and accessory circuits are off. The Blue/White mute lead from the STARMOD1 was connected to the Blue/White trigger wire of the STARRELAY and the paired black speaker output leads of the STARMOD1 were connected to one input of the STARRELAY. The LF speaker output of our aftermarket deck was connected to the other input of the STARRELAY. Last, we connected the audio output of the STARRELAY to the LF factory speaker in the pickup.

We were fortunate in that our choice of aftermarket deck permitted a connection of the Blue/White mute output of the STARMOD1 to the Stereo Mute input wire of the deck. This meant that when the OnStar system activates, the deck automatically mutes. Some aftermarket components require a connection to chassis ground for muting. In this case, simply use a relay or transistor to convert the STARMOD1's +12 volts into a ground for muting.

To test the STARMOD1 and STARRELAY, we pulled the pickup out of the shop, cranked up the stereo, and pushed the blue On-Star button. In a few seconds, the stereo system muted, and the OnStar operator could be heard in the LF speaker. The audio level was adjusted and we explained that we were testing the system. That's it.

The OnStar system is very successful, and will certainly expand in the future. Thanks to Soundgate's STARMOD1 and STARRELAY accessories, the features and benefits of OnStar will be available to even more car audiophiles.